The invention concerns a device for adjusting ramps on ferries, floating bridges or the like, in which the bridge support and the ramps forming the connection to the bank are connected to one another pivotably via a pivot point.
In particular for the bridging of shallow bank inclines, a ramp of adequate length that connects the bridge support to the bank is required. With a bending-resistant connection of the ramp to the floating bridge support, the great supporting length of this ramp leads to bending moments, which may assume undesirably high values or even inadmissibly high values.
A device for limiting the bending moment is known from DE 31 04 361 C2. In the area of the pivot point in which the ramp is pivotably connected to the bridge support there is arranged a differential cylinder, which serves for adjusting the ramp incline. For raising the ramp, hydraulic medium is fed to the cylinder chamber on the head side and hydraulic medium is thereby displaced out of the cylinder chamber on the rod side. For lowering the ramp, hydraulic medium is displaced out of the cylinder chamber on the head side and hydraulic medium is fed to the cylinder chamber on the rod side. If the ramp resting on the bank is subjected to loading, the pressure in the cylinder chamber on the rod side increases in a way corresponding to the loading. In this case, the pressure in the cylinder chamber on the rod side is a measure of the bending moment. Flanged onto the cylinder chamber on the rod side is a pressure limiting valve, which serves as a safety valve and is connected via a first line to the cylinder chamber on the rod side of a second differential cylinder. The cylinder chamber on the head side of the second differential cylinder is connected via a second line to the cylinder chamber on the head side of the first differential cylinder. If the bending moment, and consequently the pressure in the cylinder chamber on the rod side, exceeds a predetermined value, the pressure limiting valve responds. Hydraulic medium now flows out of the cylinder chamber on the rod side of the first differential cylinder into the cylinder chamber on the rod side of the second differential cylinder and displaces the piston of the latter. The hydraulic medium thereby displaced out of the cylinder chamber on the head side of the second differential cylinder is fed to the cylinder chamber on the head side of the first differential cylinder via the second line. In order that the ramp does not lift off the bank when relieved of the load following loading, provided parallel to the pressure limiting valve is a check valve, the direction of flow of which is opposite to that of the pressure limiting valve. If the ramp is relieved of load again, its own weight causes hydraulic medium to be displaced out of the cylinder chamber on the head side of the first differential cylinder into the cylinder chamber on the head side of the second differential cylinder. The hydraulic medium thereby displaced out of the cylinder chamber on the rod side of the second differential cylinder is fed via the check valve to the cylinder chamber on the rod side of the first differential cylinder. With this device it is possible to limit the bending moment. If--as in the known device--a differential cylinder is used for adjusting the ramp, means for volume equalization of the hydraulic medium are required. In the known device, the volume equalization takes place via the second differential cylinder, which has the same dimensions as the first differential cylinder. This solution is expensive, since the additional differential cylinder is required only for the volume equalization. The additional differential cylinder needs considerable space; furthermore the free end of its piston rod must be secured in such a way that it does not constitute a hazard. In the event of leakage losses between piston and inner wall of the differential cylinder, there is also the risk that the volume equalization is not permanently ensured in spite of identical differential cylinders. The use described in DE 31 04 361 C2 of a single differential cylinder for adjusting the ramp incline cannot be simply transferred to the use of two differential cylinders arranged in parallel for adjusting the ramp incline, since the pressure limiting valve can be directly flanged only onto one of two differential cylinders for adjusting the ramp incline.